The invention relates to a tangential belt drive for a plurality of similar work units for the production of twisted or twined yarns. These units are subdivided into sections, each of which has a tangential belt for driving the units. The number of units in each section is so established that the tangential belt has a width between 7 and 15 mm and a thickness between 2 and 2.7 mm. An arrangement of this type is reported in co-pending U.S. patent application Ser. No. 887,101 filed 10 July 1986, now U.S. Pat. No. 4,730,448.
Work units are defined as machine elements with high rotational speed. For instance, these units may be spindles in spinning- or twisting machines, or rotors and opening rollers in open-end spinning machines.
In this construction mentioned above it has already been proposed that the work units of the machine be driven in groups each by one of several endless tangential belts. Each tangential belt can be hereby driven by a motor. The guiding rollers of neighboring tangential belts are corotationally connected to each other thereby creating a frictional contact between the respectively neighboring tangential belts. As a result there is insured at least an approximately synchronous run of the tangential belts and that this goal can be reached under certain production conditions. So, for instance, at the start and conclusion of a run, the machine might require a redistribution of energy between the working elements and groups of working elements with different starting and tapering-off characteristics, so as to achieve an at least approximately synchronous run of the energy-releasing and energy-receiving working elements. Such differences in starting and stopping characteristics can, for instance, result from groups being of various size formed by working units of the same type. Alternatively, these differences can occur when an at least approximate synchronization between different types of work units is sought; for instance, beween spindles of a ring spinning frame, on the one hand, and the drafting mechanism, on the other hand.
Of course, there will always be a tendency to insure the required synchronous run even in starting and stopping stages through corresponding control of the drive motors, so that the mechanical coupling of the groups of work elements via the tangential belts has to effect solely the fine-tuning of the rotational speeds. However, particularly when under special conditions, such as power failures, the corresponding control of the motors is no longer possible, the frictional contact created by the corotational connection between the guide rollers has to be strong enough to produce the required synchronization.
An essential factor determining the strength of this friction contact is the contact angle at which the tangential belt wraps around its guide rollers. The sum of all contact angles at all guide points of a tangential belt guided only in one direction is, as can be seen from FIG. 1, equal to 360.degree.. This angle sum can be distributed differently over the various guiding elements, in function of their arrangement, but will always remain equal to 360.degree..
As can be seen from FIG. 1, 180.degree. of the 360.degree., which means one half, is always assigned for the guiding at both return points of the tangential belt. At the right drive-side end, the two guide rollers and the drive pulley divide between them this 180.degree. deflection. It has become obvious, that hereby, corresponding to the division of the angle sum, either the contact angle on the roller or the contact angle on the pulley become too small to insure the required friction contact especially under extreme situations.
It is therefore the object of the present invention to increase the frictional contact between the tangential belts, on one hand, and the guide rollers and the drive pulley on the other hand. Another object is to improve this way the energy transmission from the motor to the tangential belts, as well as between the tangential belts.